"People understand that prices have to rise," says the AA's Paul Watters on research showing parking charges on the rise, but he adds: "We don't want prices that shock."

Drivers said there were not enough parking places

"Sudden, big unexplained rises are a big worry for motorists," Mr Watters, head of public affairs for the motoring organisation, told the BBC News website.

He was speaking after figures collated for Direct Line Car Insurance indicated that the cost of parking a car has risen by an average of 25% in the UK in the past six years.

In some areas the costs went up from just 10p or 20p for two hours' parking to £1 or £2.

The insurance firm said areas outside the capital had suffered the biggest rises. However, Londoners still spent the most on parking - splashing out more than £7 for two hours' parking in several areas.

Mr Watters said there were numerous reasons behind car parking charges and rises, which were mainly to do with the policies of different local authorities who set them.

"Some will be playing catch up when they raise charges, while others will be trying to keep them stable under economic pressure from retailers," he went on.

"Different authorities have different policies."

'Proven method'

He said parking charges were also a "proven method" of dealing with traffic congestion in towns and cities as well as being a good source of revenue for councils.

"People don't like price hikes, especially season-ticket prices where commuters have no other way of getting into work," he stressed. "It's a worrying thing for people."

Most expensive and cheapest two-hour charges

Westminster, London..£7.99

Islington, London.....£7.32

Heathrow, London..£7.02

Biggin Hill, Kent...20p

Bramhall, Cheshire...20p

Cheadle, Gtr Manchester...20p

Source: Direct Line

Direct Line also conducted a survey which suggested one in five, or 17% of drivers, had been hit by parking fines in the past two years.

Its online survey of 2,468 drivers suggested high parking prices led 24% of motorists to knowingly park illegally, at an average cost of £74 a time.

Half of those who admitted trying to avoid parking costs said it was because the costs were too high, while 13% told the firm it was because they simply could not afford to pay.

Three-quarters of those surveyed said there were not enough parking spaces in the UK for the country's 32m motorists.

A lack of spaces had forced 22% to park illegally, the survey found.

Law breaking

Emma Holyer, Direct Line's motor spokeswoman, said: "Parking is a bone of contention for most drivers in the UK and our research shows that because of rocketing costs and limited spaces drivers are literally forced to wittingly break the law - and consequently be hit with fines in the process."

She added: "If you are driving into a busy place, it's worthwhile doing some research to find out about any 'park and ride' schemes or any cheap car parks in advance as it could save you serious money."

The AA's Mr Watters also believed there was a lack of car parking spaces.

"There have been an extra 5.8m cars on the streets in 10 years across the UK - its not surprising there's a shortage of spaces," he said.

He believes many factors are behind the rise in car ownership, including the flexibility enjoyed, a lack of faith in public transport and greater affluence.

Mr Watters said the AA would like to see more "park and ride" schemes and additional safe and secure car parks.

He also said councils should have a good strategy regarding their charges - finding a solution was "all about balance" between the interests of motorists, retailers and the need to reduce congestion, as well as other issues.